Every type of soil in every area is unique. Some are dense and strong, while others retain water well but cannot support heavy loads. The soils found across different regions of Thailand also vary depending on local geography and landforms. Despite these differences, all soils share key characteristics known as “Important Soil Properties in Construction.” These are the fundamental parameters that engineers analyze before starting any construction project whether it’s a house, building, or roadway.
Let’s explore 5 Essential Soil Properties in Construction! (Part 1) to deepen our understanding because “understanding the soil” is the “fundamental starting point in construction” that every engineer should know.
Table of Contents
1. Total Unit Weight
The unit weight of soil is classified into four types:
- Dry Unit Weight
- Wet Unit Weight
- Saturated Unit Weight
- Submerged Unit Weight
This value represents the overall weight of soil per unit volume and is a key factor for calculating vertical stress in natural soil layers at various depths. The higher the unit weight, the denser and potentially stronger the soil tends to be.
If the land was a pond, the soil may be soft. This will increase the chance that the house collapses in the future.
2. Void Ratio
The void ratio expresses the ratio of the volume of voids (air and water spaces) to the volume of solid particles in the soil. It indicates how much empty space exists between soil particles. A higher void ratio means more voids—suggesting the soil may be more compressible and prone to settlement.
3. Permeability
Since soil consists of solid particles, water, and air, understanding how water flows through soil is essential in design. Engineers evaluate permeability to study groundwater flow behavior especially for projects like retaining walls, dams, and deep excavations.
This property represents the rate at which water can flow through soil:
• High permeability (e.g., sandy or gravelly soils) → Water drains quickly, settlement occurs faster, and stability is usually achieved sooner.
• Low permeability (e.g., clay soils) → Water is retained longer, causing slow drainage and prolonged settlement.
4. Compressibility
Compressibility describes how much soil volume decreases under load or pressure. Because soil consists of discrete particles, loading causes rearrangement and compression of these particles.
- High compressibility means the soil contains large voids and low strength—making it more prone to settlement.
- Low compressibility means the soil has well-packed particles with fewer voids, resulting in better strength and load-bearing capacity.
Engineers assess compressibility based on particle arrangement, interparticle forces, and the soil’s physical and chemical properties.
5. Shear Strength
Shear strength is determined from laboratory tests on undisturbed soil samples collected during site investigation. It represents the soil’s ability to resist shear stress, which is the main cause of soil failure.
High shear strength indicates strong, stable soil with good resistance to failure. Conversely, low shear strength suggests weak soil that is more susceptible to slope failure or structural instability.
Conclusion
While soil has many properties, these five serve as the foundation for understanding soil behavior. However, having favorable values in one property alone does not guarantee strong soil performance.
In geotechnical engineering, multiple parameters must be analyzed together to ensure accurate evaluation and safe design.
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